Electric cable connections of this type between a PC and a sewing machine are generally known. They serve to enable data transmission between the PC and the sewing machine. However, data transmission is guaranteed only if a suitable voltage level is applied to the device receiving the data.
If the PC has an RS 232 C port, it is designed for a voltage level of -15 V to +15 V. Since the sewing machine used is equipped with a TTL (transistor transistor logic) logical unit, and thus it carries a voltage level of 0 to +5 V at its port, an additional port on the sewing machine, which would have to be designed for a voltage level of -15 V to +15 V, would be required for using a standard cable connection between the two devices. However, this requires an additional expense in connection with the manufacture of the sewing machine. Since such a PC port is used only in a small percentage of the sewing machines sold, such an increase in the cost of manufacture is not acceptable.